The invention relates generally to wind turbines and more specifically to a method for removing and replacing equipment in a wind turbine tower.
A wind turbine tower (WTT) is a large structure, sometimes extending to significant heights to accommodate large wind turbine rotor blades and to strategically place the rotor blades within a wind path. For example, a typical tower may have a height as high as about 100 meters (m). Such a tower may include multiple sections, often a bottom, a middle and a top section. The length and number of individual sections may vary according to the application and height of the structure. At various heights of the wind turbine tower, landings are provided. The landings include openings for ladders to allow operators and maintenance personnel to climb between landings. The landings may also include openings above each other to allow small components, tools and equipment to be lifted from a base of the wind turbine tower to a top landing of the tower.
Mounted on top of the support tower for wind turbines is a nacelle. The nacelle houses, or encloses, the equipment and components of the wind turbine and includes hubs for the wind turbine blades and the power train including the bearing, gearbox and electrical generator for the wind turbine.
FIG. 1 illustrates an exemplary wind turbine tower. Nacelle 102 is mounted atop a tall tower 104, only a portion of which is shown in FIG. 1. Wind turbine 100 also comprises a rotor 106 that includes one or more rotor blades 108 attached to a rotating hub 110. Although the wind turbine 100, as illustrated includes three rotor blades 108, there are no specific limits on the number of rotor blades.
FIG. 2 illustrates an exemplary internal arrangement for various components housed in nacelle 102. In some configurations, one or more microcontrollers within control panel 112 comprise a control system used for overall system monitoring and control. In some configurations, a variable blade pitch drive 114 is provided to control the pitch of blades 108 (not shown in FIG. 2) that drive hub 110 as a result of wind. In some configurations, the pitch angles of blades 108 are individually controlled by blade pitch drive 114. Hub 110 and blades 108 together comprise wind turbine rotor 106.
The drive train of the wind turbine includes a main rotor shaft 116 connected to hub 110 via main bearing 130. Gearbox 118 drives a high-speed shaft of generator 120. In other configurations, main rotor shaft 116 is coupled directly to generator 120. The high-speed shaft (not identified in FIG. 2) is used to drive generator 120, which is mounted on mainframe 132. In some configurations, rotor torque is transmitted via coupling 122. A meteorological boom 128 provides information for a turbine control system, which may include wind direction and/or wind speed.
Yaw drive 124 and yaw deck 126 provide a yaw orientation system for wind turbine 100. In some configurations, the yaw system is mounted on a flange provided atop tower 104.
Typically, a yaw bearing is mounted to the top section of the tower. A bedplate supporting the weight of the power train rotates on the yaw bearing, allowing wind turbine controls to rotate the nacelle to better position the blades wind respect to the wind direction for optimizing performance. A center access is provided above the topmost landing of the WTT into the nacelle.
The electrical controls for a yaw drive system may include multiple electric drive motors 136. Each electric drive motor 136 may be mounted on a yaw drive 124, which includes an internal gear train connecting the electric drive motor to a pinion gear. FIG. 2 illustrates two yaw drives with view of two additional yaw drives blocked by the main bearing 118 and main shaft 116. The pinion gear of the yaw drive engages the yaw gear, allowing for rotation of the yaw bearing and the nacelle. In certain embodiments, four yaw drives may be provided for the yaw gear. Operation of the electric drive motors 136 and thus positioning of the nacelle and the wind turbine blades relative to the wind is provided by a wind turbine control system.
Failure of one or more yaw drives may prevent the nacelle and hence the wind turbine blades from being correctly positioned with respect to the wind by the wind turbine control system.
A yaw drive may weigh about 1100 lbs, which makes it too heavy for manual movement in the nacelle and also an overload for the light-load installed permanent tower winch that are available in some wind towers. Conventional practice is to remove a yaw drive through a top hatch 139 of the nacelle 102 or through a larger opening, a nacelle lid 140, depending on the size of the yaw drive. The lift may be performed by a large site crane, capable of reaching above the top of the wind turbine tower from the ground. Use of the site crane is expensive and results in delays with crane availability. An alternate practice is to provide a crane (not shown) that may be mounted within the nacelle 102, but which extends outside a top of the nacelle and is capable of lifting the yaw drive. An access port 141 on top of the nacelle is opened to allow the erection of the crane. The hatch 139 on top of the nacelle is opened to provide a lifting path for removal of the yaw drive. A second crane may be required within the nacelle to lift the yaw drive off its foundation and move to a location for a vertical lift through the hatch 139. Once the yaw drive has cleared the top of the nacelle, the crane arm may move the yaw drive outside the envelope of the wind tower and lower the yaw drive to the ground.
Lifting operations for equipment from the nacelle and external to the tower expose the operators and the equipment inside the nacelle to environmental conditions. High winds make these external lifts dangerous for personnel and for equipment. Safety requirements strictly limit wind velocity allowable during the outside lifts. Since windfarms are generally selected based on availability of wind for driving the blades, significant delays can be encountered while waiting for acceptable conditions. Such delays result in a waste of manpower and lost operating time for the wind turbine resulting in added expense and loss of electrical power revenues.
Accordingly, there is a need to provide a safe, simple, timely, and cost-effective method for replacing articles of wind turbine equipment in the nacelle.